HOW DO WE KNOW HUMANS CAUSE GLOBAL WARMING?
Many are still asking is current global warming natural or human caused? The idea that global warming is natural is not an absurd question. In the natural cycle, global warming is natural. The better question is, 'is current global warming natural'? There are multiple lines of evidence that point us to the origin of our current warming:
Greenhouse gases trap infrared heat energy.
The isotopic signature clearly shows that the extra CO2 in the atmosphere is from fossil fuels.
We are no longer in the natural cycle. We have largely departed from the natural course of climate and there is no natural mechanism that explains it.
The models and the observations match.
There is simply no other mechanism that can explain the significantly altered climate path and the changes in the radiative forcing other than human causes.
To understand why 'this current' global warming is human caused and not natural cycle, one needs to get an idea of what the natural cycle is and what are the basic mechanisms that cause climate change in the natural cycle. The absolute essentials that you need to understand are the drivers:
Greenhouse Gases
Milankovitch Cycles
To get a more detailed understanding of the mechanisms, you need to learn a little about:
Radiative Forcing
Natural Variability
Climate Feedbacks
Climate Models
Weather vs. Climate
The National Academy of Sciences, National Research Council, Board on Atmospheric Science and Climate Present: